1. Field of the Invention
The present invention relates generally to demodulation of binary-phase modulated signals having a variable clock rate and, more particularly, to a demodulation technique for recovering data from a magnetically encoded strip on a card as the card is manually inserted into a card reader at a variable insertion speed.
2. Decription of the Prior Art
In the field of magnetic card readers, two basic techniques have been utilized in the prior art. A first technique is to provide the data on a single magnetic track and to provide a means, such as a motor drive, to move the card past a reading head at a uniform rate which matches an internal data reading clock to the rate at which data is encoded on the magnetic stripe. Card readers utilizing this technique require regulated motor drives and card reading mechanisms which are relatively costly both initially and to maintain.
A second basic prior art technique is to provide a card reader in which the card is manually inserted and to provide a second synchronizing clock track on the card which synchronizes the internal data reading clock with the rate at which the card is inserted into the reader. This technique is also costly in that, not only are two magnetic tracks required, but two data reading heads are necessary to detect both the recorded data and the recorded clock synchronizing pulses.
Thus, there has long been a need for an asynchronous data reading technique which would permit reading data from a single magnetic stripe on a card as the card was manually inserted into a card reader. The present invention satisfies that need.